This invention relates to magnetic devices, and more particularly, to write heads for use in disk drives.
Thin film recording heads include a writer and a reader that respectively record and detect magnetic domains in a disk that spins below the head. The writer in a conventional recording head includes a soft ferromagnetic yoke that is wrapped around a coil of one or more turns. Writers operate by passing an electrical current through the coil, which produces a magnetic field that aligns the yoke magnetization along the field direction. The magnetization rotates such that, for a longitudinal writer, a magnetic field extends mainly between the pole tips but also partly into the media. For a perpendicular writer, a soft underlayer is typically employed such that the write field extends between the pole tip and soft underlayer. When the write field exceeds the coercivity and demagnetization field of the media, a domain forms with its magnetization aligned along the write field direction. These domains form the bits of digital data that are detected with the read head.
There has been steady improvement in the performance of thin film recording heads as the areal density of data in magnetic storage media has increased. However, there has been a striking difference between the evolution of the reader and that of the writer. The read head has undergone major technological changes as the industry has moved from inductive to magnetoresistive and giant magnetoresistive heads. In contrast, the write head has merely evolved using the same basic coil and yoke technology. The yoke length has decreased, the number of coils has been reduced, the pole tips have become narrower. But, the fundamental design and operation of the writer is the same. The writer includes a yoke in which the magnetization is driven by the field from a current-carrying wire.
The traditional writer design continues to meet the goals of high-density recording, but the physical limits of conventional technology are being seriously tested. For areal data densities of 100 Gbit/in2, the National Storage Industry Consortium design specifies a bit size of roughly 40 nm along the track direction and 150 nm in the cross track direction. One of the preliminary proposals for 1 Tbit/in2 data density has targeted bit sizes of 14 nm long by 47 nm wide. These areal densities require the pole tip on the write head to have an extremely narrow track-width. The 1 Tbit/in2 specification for the write width is 38 mn. Furthermore, the requirement of thermal stability will necessarily mean that high-anisotropy media will be used, which in turn will need much larger write fields in order to record bits. Hence, these design parameters impose many challenges. The narrowing of the track width will necessarily reduce the cross-sectional area of the writer pole tip. This will increase the yoke reluctance and, consequently, decrease the writer efficiency. A drop in efficiency will require a larger write current. However, the write current cannot be made arbitrarily large without producing undesirable levels of Joule heating. Furthermore, it is difficult and expensive to produce large-amplitude current pulses with fast rise times. In addition, the use of high-moment materials in the writer requires larger write currents to switch the magnetization, in comparison to heads made with softer, lower moment alloys. This is because high-moment ferromagnetic materials tend to be harder magnetically than lower moment alloys, such as NiFe.
Magnetic excitation by spin transfer has been proposed for use in data storage devices. U.S. Pat. No. 5,695,864 discloses a means of dynamically remagnetizing or magnetically exciting a very thin ferromagnetic film, without the use of an externally applied magnetic field. Electrons flow through a free or excitable magnet, or reflect from it, to make its magnetization respond. To accomplish this, the spin vectors of the flowing electrons must be preferentially polarized by an auxiliary ferromagnet, whose moment orientation is fixed. The electrons flow between the fixed and free ferromagnets through a non-magnetic metallic spacer which is thick enough to make the static inter-magnetic exchange coupling negligible. While transmitting through or reflecting from the free ferromagnet, the spins of the moving electrons interact by quantum-mechanical exchange with the local, permanently present, spontaneously-polarized electron spins of the free magnet. This interaction causes a transfer of vectorial angular momentum between the several metallic layers in the device which causes the magnetization vector of the free magnet to change its direction continually with time. Thus excited, the magnetization vector will precess about its original axis. The precession cone angle will either attain a new equilibrium value which will be sustained by the current or will increase beyond 90xc2x0 and precess with decreasing amplitude until the magnetization vector has reversed by 180xc2x0 from its initial direction (i.e., switched). Information is stored in a disk by passing current between a write stylus and the disk.
There is a need for a magnetic write head that can overcome the limitations of existing write heads to achieve increased areal data densities in magnetic recording media.
A write head for a disk drive constructed in accordance with this invention includes a first layer of magnetic material having a fixed magnetization aligned in a first direction, a second layer of magnetic material having a changeable magnetization aligned in a quiescent state in a second direction orthogonal to the first direction, a first non-magnetic layer position between the first layer of magnetic material and the second layer of magnetic material, means for connection to a current supply for passing an electric current through the first layer of magnetic material, the first non-magnetic layer, and the second layer of magnetic material for switching the changeable magnetization of the second layer, and means for positioning a first edge of the second layer of magnetic material adjacent to a magnetic recording medium, whereby the magnetization of the second layer of magnetic material affects magnetization of the magnetic recording medium.
The invention also encompasses a method of writing to a magnetic storage media using the write head. The method includes the steps of providing a write head including a first layer of magnetic material having a fixed magnetization aligned in a first direction, a second layer of magnetic material having a changeable magnetization aligned in a quiescent state in a second direction orthogonal to the first direction, a non-magnetic layer positioned between the first layer of magnetic material and the second layer of magnetic material, positioning the write head adjacent to a magnetic storage media such that the second layer of magnetic material lies in a plane perpendicular to a surface of the magnetic storage media, and passing an electric current through the write head, thereby changing the direction of magnetization of the second layer of magnetic material and producing fringing magnetic flux for recording information bits in the magnetic storage media.
More generally the invention provides a method of recording information in a magnetic storage medium comprising the steps of positioning a layer of magnetic material in a plane perpendicular to a surface of the magnetic storage medium, and changing the magnetization of the layer of magnetic material through spin transfer to produce fringing magnetic flux for recording information bits in the magnetic storage media.